Internal high hardness type pearlitic rail with excellent wear resistance, rolling contact fatigue resistance, and delayed fracture property and method for producing same

ABSTRACT

An internal high hardness type pearlitic rail has a composition containing 0.73% to 0.85% by mass C, 0.5% to 0.75% by mass Si, 0.3% to 1.0% by mass Mn, 0.035% by mass or less P, 0.0005% to 0.012% by mass S, 0.2% to 1.3% by mass Cr, 0.005% to 0.12% by mass V, 0.0015% to 0.0060% by mass N, and the balance being Fe and incidental impurities, wherein the value of [% Mn]/[% Cr] is greater than or equal to 0.3 and less than 1.0, where [% Mn] represents the Mn content, and [% Cr] represents the Cr content, and the value of [% V]/[% N] is in the range of 8.0 to 30.0, where [% V] represents the V content, and [% N] represents the N content, and wherein the internal hardness of a rail head is defined by the Vickers hardness of a portion located from a surface layer of the rail head to a depth of at least 25 mm and is greater than or equal to 380 Hv and less than 480 Hv.

RELATED APPLICATIONS

This is a §371 of International Application No. PCT/JP2008/056273, withan international filing date of Mar. 25, 2008 (WO 2009/047926 A1,published Apr. 16, 2009), which is based on Japanese Patent ApplicationNo. 2007-264826, filed Oct. 10, 2007, the subject matter of which isincorporated by reference.

TECHNICAL FIELD

This disclosure relates to an internal high hardness type pearlitic railwith excellent wear resistance and rolling contact fatigue (RCF)resistance and a method for producing the same. Specifically, thedisclosure relates to an internal high hardness type pearlitic railhaving excellent wear resistance, rolling contact fatigue resistance,and delayed fracture properties and achieving longer operating life ofrails used under severe high-axle load conditions like foreign miningrailways in which freight cars are heavy and high curve lines are oftenpresent, and to a method for producing the internal high hardness typepearlitic rail.

BACKGROUND

In high-axle load railways mainly transporting mineral ores, a load onan axle of a freight car is significantly higher than that of apassenger car, and the use environment of rails is also severe. Railsused in such an environment have been mainly composed of steel having apearlitic structure from the viewpoint of significant concern of wearresistance. To enhance the efficiency of railway transport, progress hasrecently been made in increasing carrying capacity. Thus, there is aneed for further improvement in wear resistance and rolling contactfatigue resistance. High-axle load railways are used to indicaterailways in which trains and freight cars have a large carrying capacity(for example, a carrying capacity of about 150 ton or more per freightcar).

In recent years, various studies have been conducted to further improvewear resistance. For example, in Japanese Unexamined Patent ApplicationPublication Nos. 8-109439 and 8-144016, the C content is increased tomore than 0.85% and 1.20% by mass or less. In Japanese Unexamined PatentApplication Publication Nos. 8-246100 and 8-246101, the C content isincreased to more than 0.85% to 1.20% by mass or less and a rail head issubjected to heat treatment. In this way, for example, a technique forimproving wear resistance by increasing the C content to increase thecementite ratio has been used.

Meanwhile, rails placed in curved sections of high-axle load railwaysare subjected to rolling stress due to wheels and slip force due tocentrifugal force, causing severe wear of rails and fatigue damage dueto slippage. As described above, in the case where the C content issimply more than 0.85% and 1.20% by mass or less, a proeutectoidcementite structure is formed depending on heat treatment conditions,and the amount of a cementite layer in a brittle lamellar pearliticstructure is also increased. Hence, rolling contact fatigue resistanceis not improved. Japanese Unexamined Patent Application Publication No.2002-69585 thus discloses a technique for inhibiting the formation ofproeutectoid cementite by addition of Al and Si to improve rollingcontact fatigue resistance. The addition of Al, however, causes theformation of an oxide acting as a starting point of fatigue damage, forexample. It is thus difficult to satisfy both wear resistance androlling contact fatigue resistance of a rail having a pearliticstructure.

To improve the operating life of rails, in Japanese Unexamined. PatentApplication Publication No. 10-195601, a portion located from thesurface of corners and of the top of the head of the rail to a depth ofat least 20 mm have a hardness of 370 HV or more, thereby improving theoperating life of the rail. In Japanese Unexamined Patent ApplicationPublication No. 2003-293086, by controlling a pearlite block, a portionlocated from the surface of corners and of the top of the head of therail to a depth of at least 20 mm have a hardness of 300 HV to 500 HV,thereby improving the operating life of the rail.

Further strengthening of a rail increases the risk of causing a delayedfracture. In Japanese Unexamined Patent Application Publication Nos.8-109439, 8-144016, 8-246100, 8-246101, 2002-69585, 10-195601, and2003-293086, the effect of preventing the delayed fracture is notsufficient.

As a technique for preventing a delayed fracture of a rail composed ofpearlitic steel (hereinafter, referred to as a “pearlitic rail”), forexample, Japanese Patent No. 3648192 and Japanese Unexamined PatentApplication Publication No. 5-287450 disclose, a technique for improvingdelayed fracture properties by subjecting high-strength pearlitic steelto heavy drawing. In the case of applying the technique to rails,disadvantageously, the use of heavy drawing increases the productioncost of rails.

The control of the figure and volume of A-type inclusions disclosed inJapanese Unexamined Patent Application Publication Nos. 2000-328190 and6-279928, Japanese Patent No. 3323272, and Japanese Unexamined PatentApplication Publication No 6-279929 is also known to be effective as atechnique for improving delayed fracture properties. In JapaneseUnexamined Patent Application Publication Nos. 2000-328190 and 6-279928,Japanese Patent. No. 3323272, and Japanese Unexamined Patent ApplicationPublication No. 6-279929, however, the figure and volume of A-typeinclusions are controlled to improve the toughness and ductility ofrails. For example, in Japanese Unexamined Patent ApplicationPublication No. 6-279928, A-type inclusions are controlled so as to havea size of 0.1 to 20 μm and in such a manner that the number of theA-type inclusions is 25 to 11,000 per square millimeter, therebyimproving the toughness and ductility of a rail. Thus, this techniquedoes not necessarily provide satisfactory delayed fracture properties.

The use environment of pearlitic rails, however, has been increasinglysevere. To improve the operating life of pearlitic rails, there has beena challenge for higher hardness, the expansion of the range of quenchhardening depth, and improvement in delayed fracture properties.

SUMMARY

We found that the addition of Si, Mn, Cr, V, and N improves the quenchhardenability index (hereinafter, referred to as “DI”) and the carbonequivalent (hereinafter, referred to as “C_(eq)”), and keeping thevalues of [% Mn]/[% Cr] and [% V]/[% N], where [% Mn] represents the Mncontent, [% Cr] represents the Cr content, [% V] represents the Vcontent, and [% N] represents the N content, within proper rangesincrease the hardness of a portion located from the surface of a railhead to a depth of at least 25 mm, as compared with hypoeutectoid-,eutectoid-, and hypereutectoid-type pearlitic rails in the related art,thereby providing an internal high hardness type pearlitic rail withexcellent wear resistance, rolling contact fatigue resistance, anddelayed fracture properties. We also provide a preferred method forproducing the internal high hardness type pearlitic rail.

We produced pearlitic rails with different proportions of Si, Mn, Cr, V,and N and have conducted intensive studies on the structure, hardness,wear resistance, rolling contact fatigue resistance, and delayedfracture properties. As a result, we found that, in, the case where thevalue of [% Mn]/[% Cr], which is calculated from the Mn content [% Mn]and the Cr content [% Cr], is greater than or equal to 0.3 and less than1.0 and where the value of [% V]/[% N], which is calculated from the Vcontent [% V] and the N content [% N], is in the range of 8.0 to 30.0,the spacing of the lamella (lamellar spacing) of a pearlite layer(hereinafter, also referred to simply as a “lamella”) is reduced, andthe internal hardness of a rail head that is defined by the Vickershardness of a portion located from a surface layer of the rail head to adepth of at least 25 mm is greater than or equal to 380 Hv and less than480 Hv, thereby improving wear resistance, rolling contact fatigueresistance, and delayed fracture properties. Furthermore, we found thatin the case where the quench hardenability index (i.e., the DI value) isin the range of 5.6 to 8.6, the carbon equivalent (i.e., the C_(eq)value) is in the range of 1.04 to 1.27, and the value of [% Si]+[%Mn]+[% Cr], which is calculated from the Mn content [% Mn], the Crcontent [% Cr], and the Si content [% Si], is in the range of 1.55% to2.50% by mass, the effect of improving wear resistance and rollingcontact fatigue resistance can be stably maintained.

We thus provide an internal high hardness type pearlitic rail withexcellent wear resistance, rolling contact fatigue resistance, anddelayed fracture properties has a composition containing 0.73% to 0.85%by mass C, 0.5% to 0.75% by mass Si, 0.3% to 1.0% by mass Mn, 0.035% bymass or less P, 0.0005% to 0.012% by mass S, 0.2% to 1.3% by mass Cr,0.005% to 0.12% by mass V, 0.0015% to 0.0060% by mass N, and the balancebeing Fe and incidental impurities, in which the value of [% Mn]/[% Cr]is greater than or equal to 0.3 and less than 1.0, where [% Mn]represents the Mn content, and [% Cr] represents the Cr content, and thevalue of [% V]/[% N] is in the range of 8.0 to 30.0, where [% V]represents the V content, and [% N] represents the N content, and inwhich the internal hardness of a rail head is defined by the Vickershardness of a portion located from a surface layer of the rail head to adepth of at least 25 mm and is greater than or equal to 380 Hv and lessthan 480 Hv.

In the internal high hardness type pearlitic rail, preferably, the valueof DI calculated from expression (1) is in the range of 5.6 to 8.6, andthe value of C_(eq) calculated from expression (2) is in the range of1.04 to 1.27,

DI=(0.548[% C]^(1/2))×(1+0.64[% Si])×(1+4.1[% Mn])×(1+2.83[%P])×(1−0.62[% S])×(1+2.23[% Cr])×(1+1.82[% V])  (1); and

C _(eq)[% C]+([% Si]/11)+([% Mn]/7)+([% Cr]/5.8)+[% V]  (2)

where [% C] represents the C content, [% Si] represents the Si content,[% Mn] represents the Mn content, [% P] represents the P content, [% S]represents the S content, [% Cr] represents the Cr content, and [% V]represents the V content of the composition.

Preferably, the value of [% Si]+[% Mn]+[% Cr] is in the range of 1.55%to 2.50, where [% Si] represents the Si content, [% Mn] represents theMn content, and [% Cr] represents the Cr content of the composition.Preferably, the composition further contains one or two or more selectedfrom 1.0% by mass or less Cu, 1.0% by mass or less Ni, 0.001% to 0.05%by mass Nb, and 0.5% by mass or less Mo.

In the internal high hardness type pearlitic rail, preferably, thelamellar spacing of a pearlite layer in the portion located from thesurface layer of the rail head to a depth of at least 25 mm is in therange of 0.04 to 0.15 μm.

Furthermore, a method for producing an internal high hardness typepearlitic rail with excellent wear resistance, rolling contact fatigueresistance, and delayed fracture properties includes hot-rolling a steelmaterial having the composition described above to form a rail in such amanner that the finishing rolling temperature is in the range of 850° C.to 950° C., and then slack-quenching the surface of the rail head from atemperature equal to or higher than a pearlite transformation startingtemperature to 400° C. to 650° C. at a cooling rate of 1.2 to 5° C./s.

A pearlitic rail having excellent wear resistance, rolling contactfatigue resistance, and delayed fracture properties can be stablyproduced compared with pearlitic rails in the related art. Thiscontributes to longer operating life of pearlitic rails used forhigh-axle load railways and to the prevention of railway accidents,providing industrially beneficial effects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a Nishihara-type rolling contact test piece usedfor evaluation of wear resistance; FIG. 1A is a plan view, and FIG. 1Bis a side view.

FIG. 2 is a cross-sectional view of a rail head and illustratespositions where Nishihara-type rolling contact test pieces are taken.

FIGS. 3A and 3B show a Nishihara-type rolling contact test piece usedfor evaluation of rolling contact fatigue resistance; FIG. 3A is a planview, and FIG. 3B is a side view.

FIG. 4 is a cross-sectional view of a rail head and illustrates aposition where a slow strain rate technique (SSRT) test piece is taken.

FIG. 5 is a cross-sectional view of the shape and dimensions of the SSRTtest piece.

FIG. 6 is a graph showing the relationship between the [% V]/[% N] valueand the rate of improvement in delayed fracture susceptibility.

REFERENCE NUMERALS

-   -   1 Nishihara-type rolling contact test piece taken from pearlitic        rail    -   1 a Nishihara-type rolling contact test piece taken from surface        layer of rail head    -   1 b Nishihara-type rolling contact test piece taken from inside        of rail head    -   2 tire specimen    -   3 rail head    -   4 SSRT test piece

DETAILED DESCRIPTION

Reasons for the conditions of an internal high hardness type pearliticrail including the composition will now be described.

C: 0.73% to 0.85% by Mass

C is an essential element to form cementite in a pearlitic structure toensure wear resistance. The wear resistance is improved as the C contentis increased. At a C content of less than 0.73% by mass, however, it isdifficult to provide high wear resistance compared with heattreatment-type pearlitic rails in the conventional art. A C contentexceeding 0.85% by mass results in the formation of proeutectoidcementite in austenite grain boundaries during transformation after hotrolling, thereby significantly reducing rolling contact fatigueresistance. Thus, the C content is set in the range of 0.73% to 0.85% bymass and preferably 0.75% to 0.85% by mass.

Si: 0.5% to 0.75% by Mass

Si is an element serving as a deoxidizer and strengthening a pearliticstructure and needed in an amount of 0.5% by mass or more. A Si contentexceeding 0.75% by mass results in a deterioration in weldability due tohigh bond strength of Si with oxygen. Further more, high quenchhardenability of Si facilitates the formation of a martensitic structurein a surface layer of the internal high hardness type pearlitic rail.Thus, the Si content is set in the range of 0.5% to 0.75% by mass andpreferably 0.5% to 0.70% by mass.

Mn: 0.3% to 1.0% by Mass

Mn reduces a pearlite transformation starting temperature to reduce alamellar spacing. Thus, Mn contributes to higher strength and higherductility of the internal high hardness type pearlitic rail. Anexcessive amount of Mn added reduces the equilibrium transformationtemperature of pearlite to reduce the degree of supercooling, increasingthe lamellar spacing. A Mn content of less than 0.3% by mass does notresult in a sufficient effect. A Mn content exceeding 1.0% by massfacilitates the formation of a martensitic structure, so that hardeningand embrittlement occur during heat treatment and welding, therebyreadily reducing the quality of the material. Furthermore, even if thepearlitic structure is formed, the equilibrium transformationtemperature is reduced, thereby increasing the lamellar spacing. Thus,the Mn content is set in the range of 0.3% to 1.0% by mass andpreferably 0.3% to 0.8% by mass.

P: 0.035% by Mass or Less

A P content exceeding 0.035% results in a deterioration in ductility.Thus, the P content is set to 0.035% by mass or less and preferably0.020% by mass or less.

S: 0.0005% to 0.012% by Mass

S is present in steel mainly in the form of A-type inclusions. A Scontent exceeding 0.012% by mass results in a significant increase inthe amount of the inclusions and also results in the formation of coarseinclusions, thereby reducing cleanliness of steel. A S content of lessthan 0.0005% by mass leads to an increase in steelmaking cost. Thus, theS content is set in the range of 0.0005% to 0.012% by mass andpreferably 0.0005% to 0.008% by mass.

Cr: 0.2% to 1.3% by Mass

Cr is an element that increases the equilibrium transformationtemperature of pearlite to contribute to a reduction in lamellar spacingand that further increases the strength by solid-solution hardening.However, a Cr content of less than 0.2% by mass does not result insufficient internal hardness. A Cr content exceeding 1.3% by massresults in excessively high quench hardenability, forming martensite toreduce wear resistance and rolling contact fatigue resistance. Thus, theCr content is set in the range of 0.2% to 1.3% by mass, preferably 0.3%to 1.3% by mass, and more preferably 0.5% to 1.3% by mass.

V: 0.005% to 0.12% by Mass

V forms a carbonitride that is dispersively precipitated in a matrix,improving wear resistance and delayed fracture properties. At a Vcontent of less than 0.005% by mass, the effect is reduced. A V contentexceeding 0.12% by mass results in an increase in alloy cost, therebyincreasing the cost of the internal high hardness type pearlitic rail.Thus, the V content is in the range of 0.005% to 0.12% by mass andpreferably 0.012% to 0.10% by mass.

N: 0.0015% to 0.0060% by Mass

N forms a nitride that is dispersively precipitated in a matrix,improving wear resistance and delayed fracture properties. At a Ncontent of less than 0.0015% by mass, the effect is reduced. A N contentexceeding 0.0060% by mass results in the formation of coarse nitrides inthe internal high hardness type pearlitic rail, thereby reducing rollingcontact fatigue resistance and delayed fracture properties. Thus, the Ncontent is in the range of 0.0015% to 0.060% by mass and preferably0.0030% to 0.0060%.

[% Mn]/[% Cr]: Greater than or Equal to 0.3 and Less than 1.0

Mn and Cr are additive elements to increase the hardness of the internalhigh hardness type pearlitic rail. In the case where an appropriatebalance between the Mn content [% Mn] and the Cr content [% Cr] is notachieved, however, martensite is formed in a surface layer of theinternal high hardness type pearlitic rail. Note that the units of [%Mn] and [% Cr] are percent by mass. When the value of [% Mn]/[% Cr] isless than 0.3, the Cr content is high. This facilitates the formation ofmartensite in the surface layer of the internal high hardness typepearlitic rail due to high quench hardenability of Cr. When the value of[% Mn]/[% Cr] is 1.0 or more, the Mn content is high. This alsofacilitates the formation of martensite in the surface layer of theinternal high hardness type pearlitic rail due to high quenchhardenability of Mn. In the case where the Mn content and the Cr contentare set in the above ranges respectively and where the value of [%Mn]/[% Cr] is greater than or equal to 0.3 and less than 1.0, theinternal hardness of the head of the rail (hardness of a portion locatedfrom the surface layer of the head of the internal high hardness typepearlitic rail to a depth of at least 25 mm) can be controlled within arange described below while the formation of martensite in the surfacelayer is being prevented. Thus, the value of [% Mn]/[% Cr] is greaterthan or equal to 0.3 and less than 1.0 and preferably in the range of0.3 to 0.9.

[% V]/[% N]: 8.0 to 30.0

V and N are important elements that form a V-based nitride serving as ahydrogen-trapping site. To form the V-based nitride, the amounts thereofadded must be controlled. The units of [% V] and [% N] are percent bymass. At a [% V]/[% N] value of less than 8.0, the V-based nitride isnot sufficiently formed, thereby reducing the number of thehydrogen-trapping sites. Thus, it is unlikely that delayed fractureproperties will be significantly improved. At a [% V]/[% N] valueexceeding 30.0, the amount of V added is increased to increase the alloycost, thereby increasing the cost of the internal high hardness typepearlitic rail. Furthermore, it is unlikely that delayed fractureproperties will be significantly improved. Thus, the [% V]/[% N] valueis in the range of 8.0 to 30.0 and preferably 8.0 to 22.0.

Internal Hardness of Rail Head (Hardness of Portion Located from SurfaceLayer of Head of Internal High Hardness Type Pearlitic Rail to Depth ofat Least 25 mm): Greater than or Equal to 380 Hv and Less than 480 Hv

An internal hardness of the rail head of less than 380 Hv results in areduction in wear resistance, thereby reducing the operating life of theinternal high hardness type pearlitic rail. An internal hardness of therail head of 480 Hv or more results in the formation of martensite,thereby reducing the rolling contact fatigue resistance of the internalhigh hardness type pearlitic rail. Thus, the internal hardness of therail head is greater than or equal to 380 Hv and less than 480 Hv. Thereason the internal hardness of the rail head is defined by the hardnessof the portion located from the surface layer of the head of theinternal high hardness type pearlitic rail to a depth of at least 25 mmis as follows: at a depth of less than 25 mm, the wear resistance of theinternal high hardness type pearlitic rail is reduced with increasingdistance from the surface layer of the rail head toward the inside,reducing the operating life. Preferably, the internal hardness of therail head is greater than 390 Hv and less than 480 Hv.

DI: 5.6 to 8.6

The value of DI is calculated from expression (1) described below:

DI=(0.548[% C]^(1/2))×(1+0.64[% Si])×(1+4.1[% Mn])×(1+2.83[%P])×(1−0.62[% S])×(1+2.23[% Cr])×(1+1.82[% V])  (1)

where [% C] represents the C content, [% Si] represents the Si content,[% Mn] represents the Mn content, [% P] represents the P content, [% S]represents the S content, [% Cr] represents the Cr content, and [% V]represents the V content. Note that the units of [% C], [% Si], [% Mn],[% P], [% S], [% Cr], and [% V] are percent by mass.

The DI value indicates quench hardenability and is used as an index todetermine whether quench hardenability is good or not. The DI value isused as an index to prevent the formation of martensite in the surfacelayer of the internal high hardness type pearlitic rail and to achieve atarget value of the internal hardness of the rail head. The DI value ispreferably maintained within a suitable range. At a DI value of lessthan 5.6, although a desired internal hardness is provided, the internalhardness is close to the lower limit of the target hardness range. Thus,it is unlikely that the wear resistance, rolling contact fatigueresistance, and delayed fracture properties will be further improved. ADI value exceeding 8.6 results in an increase in the quenchhardenability of the internal high hardness type pearlitic rail,facilitating the formation of martensite in the surface layer of therail head. Thus, the DI value is preferably in the range of 5.6 to 8.6and more preferably 5.6 to 8.2.

C_(eq): 1.04 to 1.27

The value of C_(eq) is calculated from expression (2) described below:

C _(eq)=[% C]+([% Si]/11)+([% Mn]/7)+([% Cr]/5.8)+[% V]  (2)

where [% C] represents the C content, [% Si] represents the Si content,[% Mn] represents the Mn content, [% Cr] represents the Cr content, and[% V] represents the V content. Note that the units of [% C], [% Si], [%Mn], [% Cr], and [% V] are percent by mass.

The C_(eq) value is used to estimate the maximum hardness andweldability from proportions of the alloy components added. The C_(eq)value is used as an index to prevent the formation of martensite in thesurface layer of the internal high hardness type pearlitic rail and toachieve a target value of the internal hardness of the rail head. TheC_(eq) value is preferably maintained within a suitable range. At aC_(eq) value of less than 1.04, although a desired internal hardness isprovided, the internal hardness is close to the lower limit of thetarget hardness range. Thus, it is unlikely that the wear resistance androlling contact fatigue resistance will be further improved. A C_(eq)value exceeding 1.27 results in an increase in the quench hardenabilityof the internal high hardness type pearlitic rail, facilitating theformation of martensite in the surface layer of the rail head. Thus, theC_(eq) value is preferably in the range of 1.04 to 1.27 and morepreferably 1.04 to 1.20.

[% Si]+[% Mn]+[% Cr]: 1.55% to 2.50

When the sum of the Si content [% Si], the Mn content [% Mn], and the Crcontent [% Cr] (=[% Si]+[% Mn]+[% Cr]) is less than 1.55, it isdifficult to satisfy an internal hardness of the rail head greater thanor equal to 380 Hv and less than 480 Hv. When the sum exceeds 2.50, amartensitic structure is formed because of high quench hardenability ofSi, Mn, and Cr. This is liable to cause a reduction in ductility andtoughness. Thus, the value of [% Si]+[% Mn]+[% Cr] is preferably in therange of 1.55 to 2.50 and more preferably 1.55 to 2.30. The units of [%Si], [% Mn], and [% Cr] are percent by mass.

The composition described above may further contain one or two or moreselected from 1.0% by mass or less Cu, 1.0% by mass or less Ni, 0.001%to 0.05% by mass Nb, and 0.5% by mass or less Mo, as needed.

Cu: 1.0% by Mass or Less

Like Cr, Cu is an element that further increases the strength bysolid-solution hardening. To provide the effect, the Cu content ispreferably 0.005% by mass or more. A Cu content exceeding 1.0% by mass,however, is liable to cause Cu cracking. Thus, in the case where Cu isadded, the Cu content is preferably 1.0% by mass or less and morepreferably 0.005% to 0.5% by mass.

Ni: 1.0% by Mass or Less

Ni is an element that increases the strength without reducing ductility.Furthermore, the addition of Ni together with Cu suppresses Cu cracking.Thus, when Cu is added, preferably, Ni is also added. To provide theeffect, the Ni content is preferably 0.005% or more. The Ni contentexceeding 1.0% by mass, however, results in an increase in quenchhardenability, forming martensite. This is liable to cause a reductionin wear resistance and rolling contact fatigue resistance. In the casewhere Ni is added, thus, the Ni content is preferably 1.0% by mass orless and more preferably 0.005% to 0.5% by mass.

Nb: 0.001% to 0.05% by Mass

Nb is combined with C in steel to precipitate as a carbide during andafter rolling and contributes to a reduction in pearlite colony size.This leads to significant improvement in wear resistance, rollingcontact fatigue resistance and ductility and significant contribution tolonger operating life of the internal high hardness type pearlitic rail.To provide the effects, a Nb content of 0.001% by mass or more ispreferred. At a Nb content of less than 0.001% by mass, the effect isnot sufficiently provided. At a Nb content exceeding 0.05% by mass, theeffect of improving wear resistance and rolling contact fatigueresistance is saturated, the effect is not worth the amount added. Inthe case where Nb is added, thus, the Nb content is preferably in therange of 0.001% to 0.05% by mass and more preferably 0.001% to 0.03% bymass.

Mo: 0.5% by Mass or Less

Mo is an element that increases the strength by solid-solutionhardening. To provide the effect, the Mn content is preferably 0.005% bymass or more. A Mo content exceeding 0.5% by mass is liable to cause theformation of a bainitic structure and to reduce wear resistance. In thecase where Mo is added, thus, the Mo content is preferably 0.5% by massor less and more preferably 0.005% to 0.3% by mass.

Lamellar spacing of pearlite layer in portion located from surface layerof rail head to depth of at least 25 mm: 0.04 to 0.15 μm

A reduction in the lamellar spacing of a pearlite layer increases thehardness of the internal high hardness type pearlitic rail, which isadvantageous from the viewpoint of improving wear resistance and rollingcontact fatigue resistance. A lamellar spacing exceeding 0.15 μm does noresult in sufficient improvement in these properties. Thus, the lamellarspacing is preferably 0.15 μm or less. On the other hand, for reducingthe lamellar spacing to less than 0.04 μm, a technique for reducing thelamellar spacing by improving quench hardenability is to be used. Thisis liable to cause the formation of martensite in the surface layer,thereby adversely affecting rolling contact fatigue resistance. Thus,the lamellar spacing is preferably 0.04 μm or more.

We also provide other trace elements in place of part of the usualbalance of Fe in the composition. Examples of impurities include P andO. A P content of up to 0.035% by mass is allowable as described above.An O content of up to 0.004% by mass is allowable. Furthermore, a Ticontent of up to 0.0010% is allowable, Ti being contained as animpurity. In particular, Ti forms an oxide to reduce rolling contactfatigue resistance, which is a basic property of the rail. Thus, the Ticontent is preferably controlled so as to be up to 0.0010%.

The internal high hardness type pearlitic rail is preferably produced byhot-rolling a steel material with a composition to form a rail shape insuch a manner that the finishing rolling temperature is in the range of850° C. to 950° C., and slack-quenching at least the head of the railarticle from a temperature equal to or higher than a pearlitetransformation starting temperature to 400° C. to 650° C. at a coolingrate of 1.2 to 5° C./s. The reason for a finishing rolling temperature(roll finishing temperature) of 850° C. to 950° C., a cooling rate ofthe slack quenching of 1.2 to 5° C./s, and a cooling stop temperature of400° C. to 650° C. is described below.

Finishing Rolling Temperature: 850° C. to 950° C.

In the case of a finishing rolling temperature of less than 850° C.,rolling is performed to a low-temperature austenite range. This not onlyintroduces processing strain in the austenite grains, but also causes asignificantly high degree of extension of the austenite grains. Theintroduction of dislocation and an increase in austenite grain boundaryarea results in an increase in the number of pearlite nucleation sites.Although the pearlite colony size is reduced, the increase in the numberof pearlite nucleation sites increases a pearlite transformationstarting temperature, thereby increasing the lamellar spacing of thepearlite layer to cause a significant reduction in wear resistance.Meanwhile, a finishing rolling temperature exceeding 950° C. increasesthe austenite grain size, thereby increasing the final pearlite colonysize to cause a reduction in rolling contact fatigue resistance. Thus,the finishing rolling temperature is preferably in the range of 850° C.to 950° C.

Cooling Rate from Temperature Equal to or Higher than PearliteTransformation Starting Temperature: 1.2 to 5° C./s

A cooling rate of less than 1.2° C./s results in an increase in pearlitetransformation starting temperature, thereby increasing the lamellarspacing of the pearlite layer to cause a significant reduction in wearresistance and rolling contact fatigue resistance. Meanwhile, a coolingrate exceeding 5° C./s results in the formation of a martensiticstructure, thereby reducing ductility and toughness. Thus, the coolingrate is preferably in the range of 1.2 to 5° C./s and more preferably1.2 to 4.6° C./s. Although the pearlite transformation startingtemperature varies depending on the cooling rate, the pearlitetransformation starting temperature is referred to as an equilibriumtransformation temperature. In the composition range, the cooling ratewithin the above range may be used at 720° C. or higher.

Cooling Stop Temperature: 400° C. to 650° C.

In the case of the composition and the cooling rate, to obtain a uniformpearlitic structure at a cooling rate of 1.2 to 5° C./s, it ispreferable to ensure a cooling stop temperature of at least about 70° C.lower than the equilibrium transformation temperature. A cooling stoptemperature of less than 400° C., however, results in an increase incooling time, leading to an increase in the cost of the internal highhardness type pearlitic rail. Thus, the cooling stop temperature ispreferably in the range of 400° C. to 650° C. and more preferably 450°C. to 650° C.

Next, methods for measuring and evaluating wear resistance, rollingcontact fatigue resistance, delayed fracture properties, the internalhardness of the rail head, and the lamellar spacing will be described.

(Wear Resistance)

With respect to wear resistance, most preferably, the internal highhardness type pearlitic rail is actually placed and evaluated. In thiscase, disadvantageously, it takes a long time to conduct a test. Thus,evaluation is made by a comparative test performed under simulated realconditions of rail and wheel contact with a Nishihara-type rollingcontact test machine that can evaluate wear resistance in a short time.A Nishihara-type rolling contact test piece 1 having an externaldiameter of 30 mm is taken from the rail head. The test is performed bycontacting the test piece 1 with a tire specimen 2 and rotating them asshown in FIG. 1. Arrows in FIG. 1 indicate rotational directions of theNishihara-type rolling contact test piece 1 and the tire specimen 2.With respect to the tire specimen, a round bar with a diameter of 32 mmis taken from the head of a standard rail (Japanese industrial standardrail) described in JIS E1101. The round bar is subjected to heattreatment to have a Vickers hardness of 390 HV (load: 98 N) and atempered martensitic structure. Then the round bar is processed to havea shape shown in FIG. 1, resulting in the tire specimen. Note that theNishihara-type rolling contact test piece 1 is taken from each of twoportions of a rail head 3 as shown in FIG. 2. A piece taken from asurface layer of the rail head 3 is referred to as a Nishihara-typerolling contact test piece 1 a. A piece taken from the inside isreferred to as a Nishihara-type rolling contact test piece 1 b. Thecenter of the Nishihara-type rolling contact test piece 1 b, which istaken from the inside of the rail head 3, in the longitudinal directionis located at a depth of 24 to 26 mm (mean value: 25 mm) below the topface of the rail head 3. The test is performed in a dry state at acontact pressure of 1.4 GPa, a slip ratio of −10%, and a rotation speedof 675 rpm (750 rpm for the tire specimen). The wear amount at 100,000rotations is measured. A heat-treated pearlitic rail is employed asreference steel used in comparing wear amounts. It is determined thatthe wear resistance is improved when the wear amount is at least 10%smaller than that of the reference steel. Note that the rate ofimprovement in wear resistance is calculated from {(wear amount ofreference steel−wear amount of test piece)/(wear amount of referencesteel)}×100.

(Rolling Contact Fatigue Resistance)

With, respect to rolling contact fatigue resistance, the Nishihara-typerolling contact test piece 1 having an external diameter of 30 mm and acurved contact surface with a radius of curvature of 15 mm is taken fromthe rail head. A test is performed by contacting the test piece 1 withthe tire specimen 2 and rotating them as shown in FIG. 3. Arrows in FIG.3 indicate rotational directions of the Nishihara-type rolling contacttest piece 1 and the tire specimen 2. Note that the Nishihara-typerolling contact test piece 1 is taken from each of two portions of arail head 3 as shown in FIG. 2. The tire specimen and each portion wherethe Nishihara-type rolling contact test piece 1 is taken are the same asabove. Hence, the description is omitted. The test is performed under anoil-lubricated condition at a contact pressure of 2.2 GPa, a slip ratioof −20%, and a rotation speed of 600 rpm (750 rpm for the tirespecimen). The surface of each test piece is observed every 25,000rotations. The number of rotations at the occurrence of a crack with alength of 0.5 mm or more is defined as rolling contact fatigue life. Aheat-treated pearlitic rail is employed as reference steel used incomparing rolling contact fatigue life. It is determined that therolling contact fatigue resistance is improved when the rolling contactfatigue life is at least 10% longer than that of the reference steel.Note that the rate of improvement in rolling contact fatigue resistanceis calculated from {(number of rotations at occurrence of fatigue damageof test piece−number of rotation at occurrence of fatigue damage ofreference steel)/(number of rotations at occurrence of fatigue damage ofreference steel)}×100.

(Delayed Fracture Property)

As shown in FIG. 4, a slow strain rate technique (SSRT) test piece 4having the center 25.4 mm below the top face of the rail head 3 istaken. The SSRT test piece 4 has dimensions and a shape shown in FIG. 5.The test piece is subjected to three triangle mark finish, except forscrew sections and round sections. Parallel sections are polished withemery paper (up to #600). The SSRT test piece is mounted on an SSRT testapparatus and then subjected to an SSRT test at a strain rate of3.3×10⁻⁶/s and a temperature of 25° C. in the atmosphere, obtainingelongation E₀ of the SSRT test piece in the atmosphere. An SSRT testpiece is subjected to an SSRT test in a 20 mass % ammonium thiocyanate(NH₄SCN) solution at a strain rate of 3.3×10⁻⁶/s and a temperature of25° C., obtaining elongation E₁ of the SSRT test piece in the ammoniumthiocyanate solution. Delayed fracture susceptibility (i.e., DF) used asan index to evaluate delayed fracture properties is calculated fromDF(%)=100×(1−E₁/E₀). It is determined that the delayed fractureproperties are improved when the rate of improvement in delayed fracturesusceptibility is at least 10% higher than that of a reference steel(i.e., a heat treatment-type pearlitic rail having a C content of 0.68%by mass). Note that the rate of improvement in delayed fracturesusceptibility is calculated from {(delayed fracture susceptibility oftest piece−delayed fracture susceptibility of reference steel)/(delayedfracture susceptibility of reference steel}×100.

(Internal Hardness of Rail Head)

The Vickers hardness of a portion located from the surface layer of therail head of to a depth of 25 mm is measured at a load of 98 N and apitch of 1 mm. Among all hardness values, the minimum hardness value isdefined as the internal hardness of the rail head.

(Lamellar Spacing)

Random five fields of view of each of a portion (at a depth of about 1mm) close to the surface layer of the rail head and a portion located ata depth of 25 mm are observed with a scanning electron microscope (SEM)at a magnification of 7,500×. In the case where a portion with theminimum lamellar spacing is present, the portion is observed at amagnification of 20,000×, and the lamellar spacing in the field of viewis measured. In the case where no small lamellar spacing is observed ina field of view at a magnification of 7,500× or where the cross-sectionof a lamellar structure is not perpendicular to a lamellar plane but isobliquely arranged, the measurement is performed in another field ofview. The lamellar spacing is evaluated by the mean value of thelamellar spacing measurements in the five fields of view.

EXAMPLES Example 1

Steel materials with compositions shown in Table 1 were subjected torolling and cooling under conditions shown in Table 2 to producepearlitic rails. Cooling was performed only at heads of the rails. Aftertermination of the cooling, the pearlitic rails were subject to naturalcooling. The resulting pearlitic rails were evaluated for Vickershardness, lamellar spacing, wear resistance, rolling contact fatigueresistance, and delayed fracture properties. Table 3 shows the results.The finishing rolling temperature shown in Table 2 indicates a valueobtained by measuring a temperature of the surface layer of a side faceof each rail head on the entrance side of a final roll mill with aradiation thermometer. The cooling stop temperature indicates a valueobtained by measuring a temperature of the surface layer of a side faceof each rail head on the exit side of a cooling apparatus with aradiation thermometer. The cooling rate was defined as the rate ofchange in temperature between the start and end of cooling.

The values of [% V]/[% N] were calculated from the V content and the Ncontent in 1-B to 1-N shown in Table 1. FIG. 6 shows the relationshipbetween the resulting [% V]/[% N] values and the rate of improvement indelayed fracture susceptibility shown in Table 3.

The results demonstrated the following: In the case where the [% Mn]/[%Cr] value was greater than or equal to 0.3 and less than 1.0 and wherethe [% V]/[% N] value was in the range of 8.0 to 30.0, the portionlocated from the surface layer of the rail head to a depth of at least25 mm had a hardness greater than or equal to 380 Hv and less than 480Hv, so that the wear resistance and the rolling contact fatigueresistance were improved, and the delayed fracture properties areimproved by 10% or more. In each of 1-F and 1-I, the [% V]/[% N] valueexceeded 30. In this case, further significant improvement in delayedfracture properties was not achieved.

Example 2

Steel materials with compositions shown in Table 4 were subjected torolling and cooling under conditions shown in Table 5 to producepearlitic rails. Cooling was performed only at heads of the rails. Aftertermination of the cooling, the pearlitic rails were subject to naturalcooling. Like Example 1, the resulting pearlitic rails were evaluatedfor Vickers hardness, lamellar spacing, wear resistance, rolling contactfatigue resistance, and delayed fracture properties. Table 6 shows theresults.

The results demonstrated the following: In each of 2-B to 2-L and 2-V to2-X, in the case where the amounts of Si, Mn, Cr, V, and N added wereoptimized, the [% Mn]/[% Cr] value was greater than or equal to 0.3 andless than 1.0, the [% V]/[% N] value was in the range of 8.0 to 30.0,and one or two or more components selected from Cu, Ni, Nb, and Mo wereadded in proper amounts, the wear resistance, rolling contact fatigueresistance, and delayed fracture properties were improved. Among theseexamples, in each of 2-B to 2-H and 2-V to 2-X, i.e., in the case whereof a DI value of 5.6 to 8.6 and a C_(eq) of 1.04 to 1.27, the wearresistance and the rolling contact fatigue resistance were improvedcompared with 2-I to 2-L. In 2-U, i.e., in the case of adding Ti, therolling contact fatigue resistance was reduced.

A pearlitic rail having excellent wear resistance, rolling contactfatigue resistance, and delayed fracture properties compared withpearlitic rails in the related art can be stably produced. Thiscontributes to longer operating life of pearlitic rails used forhigh-axle load railways and to the prevention of railway accidents,providing industrially beneficial effects.

INDUSTRIAL APPLICABILITY

A pearlitic rail having excellent wear resistance, rolling contactfatigue resistance, and delayed fracture properties compared withpearlitic rails in the related art can be stably produced. Thiscontributes to longer operating life of pearlitic rails used forhigh-axle load railways and to the prevention of railway accidents,providing industrially beneficial effects.

TABLE 1 (mass % excluding mass ratio, DI, and Ceq) [% Si] + Steel [%Mn]/ [% V]/ [% Mn] + No. C Si Mn P S Cr V N [% Cr] [% N] DI Ceq [% Cr]Remarks 1-A 0.68 0.18 1.00 0.014 0.016 0.20 0.000 0.0024 5.0 0.0 3.80.87 1.38 Reference material 1-B 0.81 0.52 0.71 0.011 0.006 0.82 0.0730.0035 0.9 20.9 8.5 1.17 2.05 Example 1-C 0.84 0.53 0.53 0.011 0.0030.79 0.061 0.0056 0.7 10.9 6.7 1.16 1.85 1-D 0.84 0.61 0.66 0.012 0.0040.88 0.017 0.0021 0.8 8.1 8.2 1.16 2.15 1-E 0.83 0.51 0.68 0.010 0.0040.84 0.092 0.0031 0.8 29.7 8.6 1.21 2.03 1-F 0.81 0.51 0.71 0.012 0.0050.8 0.089 0.0020 0.9 44.5 8.5 1.18 2.02 Comparative 1-G 0.82 0.51 0.730.013 0.004 0.79 0.011 0.0039 0.9 2.8 7.7 1.12 2.03 example 1-H 0.810.66 0.69 0.011 0.005 0.83 0.015 0.0022 0.8 6.8 8.1 1.13 2.18 1-I 0.820.59 0.68 0.010 0.006 0.77 0.072 0.0022 0.9 32.7 8.2 1.18 2.04 1-J 0.760.51 0.69 0.011 0.003 0.82 0.072 0.0042 0.8 17.1 8.0 1.12 2.02 Example1-K 0.83 0.70 0.63 0.013 0.003 0.79 0.055 0.0050 0.8 11.0 8.1 1.17 2.121-L 0.84 0.69 0.59 0.010 0.004 0.99 0.030 0.0030 0.6 10.0 8.6 1.19 2.271-M 0.82 0.52 0.46 0.011 0.004 1.20 0.063 0.0035 0.4 18.0 8.0 1.20 2.181-N 0.85 0.70 0.55 0.011 0.003 0.83 0.090 0.0045 0.7 20.0 8.1 1.23 2.08

TABLE 2 Finishing Cooling rolling stop Cooling temperature temperaturerate Steel No. (° C.) (° C.) (° C./s) Remarks 1-A 900 500 2.0 Referencematerial 1-B 900 500 1.6 Example 1-C 950 550 2.3 1-D 900 450 2.2 1-E 850600 3.2 1-F 900 550 1.4 Comparative 1-G 950 500 2.2 example 1-H 950 5501.9 1-I 850 500 1.6 1-J 900 500 2.6 Example 1-K 950 550 3.2 1-L 900 5002.3 1-M 850 450 2.5 1-N 900 550 3.3

TABLE 3 Surface layer of rail Number of rotations at occurrence of Rateof rolling improvement Rate of contact in rolling Inside of rail 25 mmHardness improvement fatigue contact Hardness of Lamellar Wear in weardefect fatigue of Lamellar Steel rail spacing Micro- amount resistance(×10⁵ resistance rail spacing Micro- No. (HV) (μm) structure (g) (%)rotations) (%) (HV) (μm) structure 1-A 370 0.16 P 1.37 — 8.10 — 340 0.23P 1-B 431 0.06 P 1.10 19.7 9.90 22.2 410 0.08 P 1-C 420 0.08 P 1.14 16.89.68 19.5 403 0.09 P 1-D 433 0.06 P 1.12 18.2 9.90 22.2 399 0.10 P 1-E442 0.05 P 1.09 20.4 10.13 25.1 415 0.08 P 1-F 430 0.06 P 1.10 19.7 9.9022.2 412 0.08 P 1-G 409 0.09 P 1.16 15.3 9.23 14.0 382 0.14 P 1-H 4110.08 P 1.14 16.8 9.23 14.0 384 0.14 P 1-I 436 0.05 P 1.10 19.7 9.90 22.2402 0.09 P 1-J 435 0.06 P 1.12 18.2 9.90 22.2 402 0.09 P 1-K 440 0.06 P1.11 19.0 9.90 22.2 401 0.10 P 1-L 439 0.06 P 1.12 18.2 9.68 19.5 4030.10 P 1-M 441 0.05 P 1.12 18.2 9.90 22.2 409 0.09 P 1-N 433 0.06 P 1.1416.8 9.68 19.5 399 0.10 P Inside of rail 25 mm Number of rotations atoccurrence Rate of of improvement Rate of Rate of rolling in improvementimprovement contact rolling in in fatigue contact Delayed delayed Wearwear defect fatigue fracture fracture Steel amount resistance (×10⁵resistance susceptibility susceptibility No. (g) (%) rotations) (%) (%)(%) Remarks 1-A 1.40 — 7.65 — 85.0 0.0 Reference material 1-B 1.16 17.19.23 20.7 73.7 13.3 Example 1-C 1.18 15.7 9.00 17.6 75.0 11.8 1-D 1.1716.4 9.00 17.6 76.1 10.5 1-E 1.16 17.1 9.00 17.6 72.6 14.6 1-F 1.17 16.49.23 20.7 72.4 14.8 Comparative 1-G 1.26 10.0 8.55 11.8 78.1 8.1 example1-H 1.26 10.0 8.55 11.8 76.9 9.5 1-I 1.19 15.0 9.23 20.7 72.3 14.9 1-J1.19 15.0 9.00 17.6 73.9 13.1 Example 1-K 1.18 15.7 9.00 17.6 75.2 11.51-L 1.19 15.0 9.00 17.6 75.6 11.1 1-M 1.17 16.4 9.00 17.6 75.3 11.4 1-N1.19 15.0 9.00 17.6 74.8 12.0  P represents pearlite, and M representsmartensite.

TABLE 4 (mass % excluding mass ratio, DI, and Ceq) Steel No. C Si Mn P SCr V N Nb Cu Ni 2-A 0.68 0.18 1.00 0.014 0.016 0.20 0.000 0.0032 2-B0.84 0.55 0.55 0.012 0.004 0.77 0.050 0.0021 0.03 2-C 0.84 0.65 0.390.011 0.008 0.78 0.051 0.0055 0.01 0.05 0.05 2-D 0.84 0.55 0.33 0.0110.004 1.09 0.120 0.0043 0.05 0.05 2-E 0.82 0.52 0.66 0.015 0.003 0.830.050 0.0051 0.02 2-F 0.82 0.54 0.77 0.013 0.005 0.83 0.029 0.0031 0.022-G 0.82 0.66 0.47 0.016 0.002 1.15 0.013 0.0016 0.01 0.05 2-H 0.81 0.530.72 0.012 0.007 0.86 0.055 0.0051 0.03 0.07 2-I 0.83 0.51 0.51 0.0100.005 0.65 0.031 0.0032 0.02 2-J 0.81 0.52 0.44 0.011 0.003 0.69 0.0620.0044 0.01 2-K 0.81 0.52 0.44 0.012 0.004 0.75 0.042 0.0032 0.02 2-L0.79 0.51 0.31 0.011 0.003 0.70 0.033 0.0019 0.01 2-M 0.78 0.31 0.720.011 0.004 1.08 0.044 0.0048 0.04 0.03 0.03 2-N 0.70 0.62 0.81 0.0120.004 0.89 0.031 0.0022 0.02 2-P 1.05 0.51 0.58 0.009 0.003 0.63 0.0270.0031 0.02 2-Q 0.84 0.94 0.63 0.009 0.008 0.81 0.044 0.0042 0.02 0.050.05 2-R 0.83 0.62 0.31 0.007 0.003 1.25 0.021 0.0045 0.01 2-S 0.76 0.531.16 0.011 0.004 0.50 0.081 0.0042 2-T 0.80 0.51 0.36 0.013 0.007 1.350.051 0.0041 0.05 0.05 2-U 0.79 0.73 0.55 0.011 0.004 0.75 0.055 0.00550.02 2-V 0.77 0.62 0.61 0.010 0.004 0.72 0.025 0.0031 0.01 2-W 0.84 0.510.51 0.014 0.003 0.71 0.053 0.0055 2-X 0.82 0.70 0.31 0.013 0.004 1.110.048 0.0059 0.01 0.01 [% Si] + Steel [% Mn]/ [% V]/ [% Mn] + No. Mo Ti[% Cr] [% N] DI Ceq [% Cr] Remarks 2-A 5.0 0.0 3.8 0.87 1.38 Referencematerial 2-B 0.7 23.8 6.8 1.15 1.87 Example 2-C 0.5 9.3 5.7 1.14 1.822-D 0.05 0.3 27.9 6.9 1.25 1.97 2-E 0.03 0.8 9.8 7.9 1.15 2.01 2-F 0.030.9 9.4 8.6 1.15 2.14 2-G 0.4 8.1 7.9 1.16 2.28 2-H 0.15 0.8 10.8 8.61.16 2.11 2-I 0.8 9.7 5.4 1.09 1.67 2-J 0.08 0.6 14.1 5.4 1.10 1.65 2-K0.6 13.1 5.5 1.09 1.71 2-L 0.4 17.4 4.1 1.03 1.52 2-M 0.7 9.2 8.7 1.142.11 Comparative 2-N 0.9 14.1 9.0 1.06 2.32 Example 2-P 0.04 0.9 8.7 6.51.31 1.72 2-Q 0.8 10.5 8.9 1.20 2.38 2-R 0.16 0.2 4.7 6.3 1.17 2.18 2-S0.05 2.3 19.3 9.2 1.14 2.19 2-T 0.03 0.3 12.4 7.3 1.18 2.22 2-U 0.01 0.710.0 7.0 1.12 2.03 2-V 0.8 8.1 6.6 1.06 1.95 Example 2-W 0.01 0.7 9.66.1 1.13 1.73 2-X 0.3 8.1 6.4 1.17 2.12

TABLE 5 Finishing rolling Cooling stop temperature temperature Coolingrate Steel No. (° C.) (° C.) (° C./s) Remarks 2-A 900 500 2.0 Referencematerial 2-B 900 500 2.3 Example 2-C 900 500 1.9 2-D 950 550 1.3 2-E 900500 2.2 2-F 900 500 1.9 2-G 950 500 2.3 2-H 900 600 2.0 2-I 950 500 2.02-J 850 550 2.1 2-K 950 450 2.8 2-L 950 550 2.0 2-M 900 500 2.1Comparative 2-N 900 550 2.0 example 2-P 950 500 2.2 2-Q 900 500 2.3 2-R850 450 3.1 2-S 850 650 2.4 2-T 850 550 3.2 2-U 900 600 2.2 2-V 850 5502.6 Example 2-W 900 500 2.4 2-X 900 600 2.6

TABLE 6 Surface layer of rail Number of rotations at Rate of occurrenceof Rate of improvement rolling contact improvement in Inside of rail 25mm Lamellar Wear in wear fatigue defect rolling contact Lamellar SteelHardness spacing Micro- amount resistance (× 10⁵ fatigue Hardnessspacing No. of rail (HV) (μm) structure (g) (%) rotations) resistance(%) of rail (HV) (μm) 2-A 370 0.16 P 1.37 — 8.10 — 340 0.23 2-B 425 0.08P 1.10 19.7 9.68 19.5 399 0.10 2-C 429 0.07 P 1.11 19.0 9.68 19.5 3950.11 2-D 431 0.06 P 1.10 19.7 9.68 19.5 401 0.10 2-E 428 0.07 P 1.1119.0 9.90 22.2 400 0.10 2-F 434 0.06 P 1.10 19.7 9.90 22.2 398 0.10 2-G459 0.05 P 1.07 21.9 10.58 30.6 417 0.09 2-H 438 0.05 P 1.10 19.7 10.3527.8 412 0.09 2-I 419 0.11 P 1.15 16.1 9.23 14.0 381 0.15 2-J 422 0.12 P1.14 16.8 9.00 11.1 381 0.15 2-K 425 0.08 P 1.10 19.7 9.90 22.2 383 0.142-L 411 0.09 P 1.14 16.8 9.23 14.0 380 0.15 2-M 411 0.11 P 1.17 14.69.00 11.1 377 0.17 2-N 409 0.11 P 1.14 16.8 9.00 11.1 373 0.19 2-P 4320.05 P + θ 1.11 19.0 8.78 8.4 378 0.17 2-Q 488 — P + M 1.12 18.2 8.555.6 421 0.08 2-R 483 — P + M 1.12 18.2 8.55 5.6 432 0.07 2-S 495 — P + M1.18 13.9 8.55 5.6 440 0.06 2-T 500 — P + M 1.18 13.9 8.55 5.6 437 0.062-U 412 0.11 P 1.17 14.6 8.78 8.4 388 0.15 2-V 421 0.09 P 1.13 17.5 9.6819.5 395 0.11 2-W 435 0.08 P 1.11 19.0 9.68 19.5 403 0.10 2-X 439 0.07 P1.10 19.7 9.68 19.5 409 0.09 Inside of rail 25 mm Number of rotations atRate of Rate of occurrence of Rate of improvement in improvement inrolling contact improvement in Delayed delayed Wear wear fatigue defectrolling contact fracture fracture Steel Micro- amount resistance (× 10⁵fatigue susceptibility susceptibility No. structure (g) (%) rotations)resistance (%) (%) (%) Remarks 2-A P 1.40 — 7.65 — 85.0 0.0 Referencematerial 2-B P 1.17 16.4 9.00 17.6 72.4 14.8 Example 2-C P 1.18 15.79.00 17.6 72.2 15.1 2-D P 1.17 16.4 9.00 17.6 73.1 14.0 2-E P 1.17 16.49.00 17.6 74.2 12.7 2-F P 1.18 15.7 9.00 17.6 74.2 12.7 2-G P 1.15 17.99.45 23.5 75.1 11.6 2-H P 1.16 17.1 9.45 23.5 75.1 11.6 2-I P 1.25 10.78.55 11.8 74.8 12.0 2-J P 1.25 10.7 8.55 11.8 74.5 12.4 2-K P 1.25 10.78.55 11.8 74.1 12.8 2-L P 1.26 10.0 8.55 11.8 73.9 13.1 2-M P 1.31 6.48.33 8.9 74.3 12.6 Comparative 2-N P 1.33 5.0 8.33 8.9 74.3 12.6 example2-P P 1.31 6.4 8.33 8.9 74.0 12.9 2-Q P 1.14 18.6 9.45 23.5 76.2 10.42-R P 1.10 21.4 9.68 26.5 76.2 10.4 2-S P 1.08 22.9 9.68 26.5 76.5 10.02-T P 1.10 21.4 9.45 23.5 76.3 10.2 2-U P 1.19 15.0 7.88 3.0 76.3 10.22-V P 1.21 13.6 8.78 14.8 73.9 13.1 Example 2-W P 1.17 16.4 9.00 17.674.1 12.8 2-X P 1.15 17.9 9.23 20.7 74.1 12.8  P represents pearlite, θrepresents proeutectoid cementite, and M represents martensite.

1. An internal high hardness type pearlitic rail comprising acomposition containing 0.73% to 0.85% by mass C, 0.5% to 0.75% by massSi, 0.3% to 1.0% by mass Mn, 0.035% by mass or less P, 0.0005% to 0.012%by mass S, 0.2% to 1.3% by mass Cr, 0.005% to 0.12% by mass V, 0.0015%to 0.0060% by mass N, and the balance being Fe and incidentalimpurities, wherein [% Mn]/[% Cr] is greater than or equal to 0.3 andless than 1.0, where [% Mn] represents Mn content, and [% Cr] representsCr content, and [% V]/[% N] is in the range of 8.0 to 30.0, where [% V]represents V content, and [% N] represents N content, and whereininternal hardness of a rail head is defined by Vickers hardness of aportion located from a surface layer of the rail head to a depth of atleast 25 mm and is greater than or equal to 380 Hv and less than 480 Hv.2. The internal high hardness type pearlitic rail according to claim 1,wherein DI calculated from expression (1) is 5.6 to 8.6, and C_(eq)calculated from expression (2) is 1.04 to 1.27,DI=(0.548[% C]^(1/2))×(1+0.64[% Si])×(1+4.1[% Mn])×(1+2.83[%P])×(1−0.62[% S])×(1+2.23[% Cr])×(1+1.82[% V])  (1); andC _(eq)=[% C]+([% Si]/11)([% Mn]/7)+([% Cr]/5.8)+[% V]  (2) where [% C]represents C content, [% Si] represents Si content, [% Mn] represents Mncontent, [% P] represents P content, [% S] represents S content, [% Cr]represents Cr content, and [% V] represents V content of thecomposition.
 3. The internal high hardness type pearlitic rail accordingto claim 1, wherein [% Si]+[% Mn]+[% Cr] is 1.55% to 2.50, where [% Si]represents Si content, [% Mn] represents Mn content, and [% Cr]represents Cr content of the composition.
 4. The internal high hardnesstype pearlitic rail according to claim 1, wherein the compositionfurther contains one or more components selected from the groupconsisting of 1.0% by mass or less Cu, 1.0% by mass or less Ni, 0.001%to 0.05% by mass Nb, and 0.5% by mass or less Mo.
 5. The internal highhardness type pearlitic rail according to claim 1, wherein lamellarspacing of a pearlite layer in a portion located from a surface layer ofthe rail head to a depth of at least 25 mm is 0.04 to 0.15 μm.
 6. Amethod of producing an internal high hardness type pearlitic railcomprising: hot-rolling a steel material having the compositionaccording to claim 1 to form a rail in such a manner that the finishingrolling temperature is in the range of 850° C. to 950° C.; andslack-quenching a surface of the rail head from a temperature equal toor higher than a pearlite transformation starting temperature to 400° C.to 650° C. at a cooling rate of 1.2 to 5° C./s.
 7. The internal highhardness type pearlitic rail according to claim 2, wherein [% Si]+[%Mn]+[% Cr] is 1.55% to 2.50, where [% Si] represents Si content, [% Mn]represents Mn content, and [% Cr] represents Cr content of thecomposition.
 8. The internal high hardness type pearlitic rail accordingto claim 2, wherein the composition further contains one or morecomponents selected from the group consisting of 1.0% by mass or lessCu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and 0.5% bymass or less Mo.
 9. The internal high hardness type pearlitic railaccording to claim 3, wherein the composition further contains one ormore components selected from the group consisting of 1.0% by mass orless Cu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and 0.5%by mass or less Mo.
 10. The internal high hardness type pearlitic railaccording to claim 7, wherein the composition further contains one ormore components selected from the group consisting of 1.0% by mass orless Cu, 1.0% by mass or less Ni, 0.001% to 0.05% by mass Nb, and 0.5%by mass or less Mo.
 11. The internal high hardness type pearlitic railaccording to claim 2, wherein lamellar spacing of a pearlite layer in aportion located from a surface layer of the rail head to a depth of atleast 25 mm is 0.04 to 0.15 μm.
 12. The internal high hardness typepearlitic rail according to claim 3, wherein lamellar spacing of apearlite layer in a portion located from a surface layer of the railhead to a depth of at least 25 mm is 0.04 to 0.15 μm.
 13. The internalhigh hardness type pearlitic rail according to claim 4, wherein lamellarspacing of a pearlite layer in a portion located from a surface layer ofthe rail head to a depth of at least 25 mm is 0.04 to 0.15 μm.
 14. Theinternal high hardness type pearlitic rail according to claim 7, whereinlamellar spacing of a pearlite layer in a portion located from a surfacelayer of the rail head to a depth of at least 25 mm is 0.04 to 0.15 μm.15. The internal high hardness type pearlitic rail according to claim10, wherein lamellar spacing of a pearlite layer in a portion locatedfrom a surface layer of the rail head to a depth of at least 25 mm is0.04 to 0.15 μm.